A boy is standing by the side of a railway track finds that an up train crosses him in 10 seconds and a down train of thrice the length of that of the up train crosses him in 15 seconds. How long (in seconds) will it take two trains to cross each other? |
12\(\frac{1}{3}\) 15 20 13\(\frac{1}{3}\) |
13\(\frac{1}{3}\) |
LCM of [10 & 15] = 30 Let length of up train = 30m Length of down train = 30 × 3 = 90m Speed (up train) = \(\frac{30}{10}\) = 3 m/sec Speed (down train) = \(\frac{90}{15}\) = 6 m/sec Time to cross each other = \(\frac{30 + 90}{3 + 6}\) = \(\frac{120}{9}\) = \(\frac{40}{3}\) = 13\(\frac{1}{3}\) second |